U.S. patent application number 15/674355 was filed with the patent office on 2017-11-23 for automatically determining a wet microphone condition in a sports camera.
The applicant listed for this patent is GoPro, Inc.. Invention is credited to Magnus Hansson, Zhinian Jing, Ke Li, Joyce Rosenbaum, Erich Tisch.
Application Number | 20170339320 15/674355 |
Document ID | / |
Family ID | 57683380 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170339320 |
Kind Code |
A1 |
Jing; Zhinian ; et
al. |
November 23, 2017 |
AUTOMATICALLY DETERMINING A WET MICROPHONE CONDITION IN A SPORTS
CAMERA
Abstract
An audio capture system for a sports camera includes at least
one "enhanced" microphone and at least one "reference" microphone.
The enhanced microphone includes a drainage enhancement feature to
enable water to drain from the microphone more quickly than the
reference microphone. A microphone selection controller selects
between the microphones based on a microphone selection algorithm
to enable high quality in conditions where the sports camera
transitions in and out of water during activities such as surfing,
water skiing, swimming, or other wet environments.
Inventors: |
Jing; Zhinian; (Belmont,
CA) ; Li; Ke; (San Jose, CA) ; Tisch;
Erich; (San Francisco, CA) ; Rosenbaum; Joyce;
(Mountain View, CA) ; Hansson; Magnus; (Los Altos,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GoPro, Inc. |
San Mateo |
CA |
US |
|
|
Family ID: |
57683380 |
Appl. No.: |
15/674355 |
Filed: |
August 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15083266 |
Mar 28, 2016 |
9769364 |
|
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15674355 |
|
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|
62188450 |
Jul 2, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04R 1/44 20130101; H04R
29/004 20130101; H04R 2410/07 20130101; H04R 3/00 20130101; H04R
3/005 20130101; H04N 5/2252 20130101; H04R 5/04 20130101; H04R
2499/11 20130101; G03B 17/08 20130101; H04R 2410/05 20130101 |
International
Class: |
H04N 5/225 20060101
H04N005/225; G03B 17/08 20060101 G03B017/08; H04R 3/00 20060101
H04R003/00; H04R 29/00 20060101 H04R029/00; H04R 1/44 20060101
H04R001/44 |
Claims
1. An audio capture system comprising: a first microphone including
a drainage enhancement feature structured to drain liquid; a second
microphone lacking the drainage enhancement feature; a processor;
and a non-transitory computer-readable medium storing instructions
for generating an output audio signal, the instructions when
executed by the processor causing the processor to perform steps
including: receiving a first audio signal from the first microphone
representing ambient audio captured by the first microphone;
receiving a second audio signal from the second microphone
representing ambient audio captured by the second microphone;
determining a first correlation metric between a first portion of
the first audio signal and a first portion of the second audio
signal captured during a first time interval, the correlation
metric representing a similarity between the first portion of the
first audio signal and the second portion of the second audio
signal during the first time interval; responsive to the first
correlation metric exceeding a first predefined threshold, storing
the first portion of the first audio signal as a first portion of
the output audio signal corresponding to the first time
interval.
2. The audio capture system of claim 1, the instructions when
executed further causing the processor to perform steps including:
determining a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to the
second correlation metric not exceeding the first predefined
threshold, determining if the first and second microphones are
submerged in liquid during the second time interval; responsive to
determining that first microphone the first and second microphones
are submerged during the second time interval, determining a first
noise metric for the second portion of the first audio signal and a
second noise metric for the second portion of the second audio
signal during the second time interval; selecting between storing
the second portion of the first audio signal and the second portion
of the second audio signal as a second portion of the output audio
signal corresponding to the second time interval based on the first
and second noise metrics.
3. The audio capture system of claim 2, wherein selecting between
storing the second portion of the first audio signal and the second
portion of the second audio signal comprises: selecting the second
portion of the first audio signal responsive to a sum of the first
noise metric and a bias value being less than the second noise
metric.
4. The audio capture system of claim 2, wherein selecting between
storing the second portion of the first audio signal and the second
portion of the second audio signal comprises: selecting the second
portion of the second audio signal responsive to the sum of the
first noise metric and the bias value being greater than the second
noise metric.
5. The audio capture system of claim 1, the instructions when
executed further causing the processor to perform steps including:
determining a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to
determining that the second correlation metric does not exceed the
first predefined threshold, determining whether the first
microphone is wet but is not submerged in liquid during the second
time interval; responsive to determining that the first microphone
is wet but is not submerged during the second time interval,
storing the second portion of the second audio signal as a second
portion of the output audio signal corresponding to the second time
interval.
6. The audio capture system of claim 1, the instructions when
executed further causing the processor to perform steps including:
determining a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to
determining that the second correlation metric does not exceed the
first predefined threshold, determining whether the first
microphone is wet during the second time interval; responsive to
determining that first microphone is wet during the second time
interval, determining a first noise metric for the second portion
of the first audio signal and a second noise metric for the second
portion of the second audio signal during the second time interval;
and selecting between storing the second portion of the first audio
signal and the second portion of the second audio signal as a
second portion of the output audio signal corresponding to the
second time interval based on the first and second noise
metrics.
7. The audio capture system of claim 6, wherein selecting between
storing the second portion of the first audio signal and the second
portion of the second audio signal comprises: selecting the second
portion of the first audio signal responsive to a sum of the first
noise metric and a bias value being less than the second noise
metric.
8. The audio capture system of claim 6, wherein selecting between
storing the second portion of the first audio signal and the second
portion of the second audio signal comprises: selecting the second
portion of the second audio signal responsive to the sum of the
first noise metric and the bias value being greater than the second
noise metric.
9. The audio capture system of claim 6, wherein determining if the
first microphone is wet comprises: determining a first average
signal level of the second portion of the audio signal and a second
average signal level for the second portion of the second audio
signal; determining if a wind condition is detected during the
second time interval; and responsive to a ratio of the first
average signal level to the second average signal level exceeding a
second threshold or detecting a wind condition, determining that
the first microphone is not wet.
10. The audio capture system of claim 6, wherein determining if the
first microphone is wet comprises: determining a first average
signal level of the second portion of the audio signal and a second
average signal level for the second portion of the second audio
signal; determining if a wind condition is detected during the
second time interval; and responsive to the ratio of the first
average signal level to the second average signal level not
exceeding the second threshold and not detecting the wind
condition, determining that the first microphone is wet.
11. A method for generating an output audio signal in an audio
capture system having multiple microphones including at least a
first microphone and a second microphone, the first microphone
including a drainage enhancement feature structured to drain liquid
more quickly than the second microphone lacking the drainage
enhancement feature, the method comprising: receiving a first audio
signal from the first microphone representing ambient audio
captured by the first microphone; receiving a second audio signal
from the second microphone representing ambient audio captured by
the second microphone; determining, by a processor, a first
correlation metric between a first portion of the first audio
signal and a first portion of the second audio signal captured
during a first time interval, the correlation metric representing a
similarity between the first portion of the first audio signal and
the second portion of the second audio signal during the first time
interval; responsive to the first correlation metric exceeding a
first predefined threshold, storing the first portion of the first
audio signal as a first portion of the output audio signal
corresponding to the first time interval.
12. The method of claim 1, further comprising: determining, by the
processor, a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to the
second correlation metric not exceeding the first predefined
threshold, determining if the first and second microphones are
submerged in liquid during the second time interval; responsive to
determining that first microphone the first and second microphones
are submerged during the second time interval, determining a first
noise metric for the second portion of the first audio signal and a
second noise metric for the second portion of the second audio
signal during the second time interval; selecting between storing
the second portion of the first audio signal and the second portion
of the second audio signal as a second portion of the output audio
signal corresponding to the second time interval based on the first
and second noise metrics.
13. The method of claim 11, further comprising: determining, by the
processor, a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to
determining that the second correlation metric does not exceed the
first predefined threshold, determining whether the first
microphone is wet but is not submerged in liquid during the second
time interval; responsive to determining that the first microphone
is wet but is not submerged during the second time interval,
storing the second portion of the second audio signal as a second
portion of the output audio signal corresponding to the second time
interval.
14. The method of claim 11, further comprising: determining, by the
processor, a second correlation metric between a second portion of
the first audio signal and a second portion of the second audio
signal captured during a second time interval; responsive to
determining that the second correlation metric does not exceed the
first predefined threshold, determining whether the first
microphone is wet during the second time interval; responsive to
determining that first microphone is wet during the second time
interval, determining a first noise metric for the second portion
of the first audio signal and a second noise metric for the second
portion of the second audio signal during the second time interval;
and selecting between storing the second portion of the first audio
signal and the second portion of the second audio signal as a
second portion of the output audio signal corresponding to the
second time interval based on the first and second noise
metrics.
15. The method of claim 14, wherein determining if the first
microphone is wet comprises: determining a first average signal
level of the second portion of the audio signal and a second
average signal level for the second portion of the second audio
signal; determining if a wind condition is detected during the
second time interval; and responsive to the ratio of the first
average signal level to the second average signal level not
exceeding the second threshold and not detecting the wind
condition, determining that the first microphone is wet.
16. A non-transitory computer-readable medium storing instructions
for generating an output audio signal in an audio capture system
having multiple microphones including at least a first microphone
and a second microphone, the first microphone including a drainage
enhancement feature structured to drain liquid more quickly than
the second microphone lacking the drainage enhancement feature, the
instructions when executed by a processor causing the processor to
perform steps including: receiving a first audio signal from the
first microphone representing ambient audio captured by the first
microphone; receiving a second audio signal from the second
microphone representing ambient audio captured by the second
microphone; determining a first correlation metric between a first
portion of the first audio signal and a first portion of the second
audio signal captured during a first time interval, the correlation
metric representing a similarity between the first portion of the
first audio signal and the second portion of the second audio
signal during the first time interval; responsive to the first
correlation metric exceeding a first predefined threshold, storing
the first portion of the first audio signal as a first portion of
the output audio signal corresponding to the first time
interval.
17. The non-transitory computer-readable medium of claim 16, the
instructions when executed further causing the processor to perform
steps including: determining a second correlation metric between a
second portion of the first audio signal and a second portion of
the second audio signal captured during a second time interval;
responsive to the second correlation metric not exceeding the first
predefined threshold, determining if the first and second
microphones are submerged in liquid during the second time
interval; responsive to determining that first microphone the first
and second microphones are submerged during the second time
interval, determining a first noise metric for the second portion
of the first audio signal and a second noise metric for the second
portion of the second audio signal during the second time interval;
selecting between storing the second portion of the first audio
signal and the second portion of the second audio signal as a
second portion of the output audio signal corresponding to the
second time interval based on the first and second noise
metrics.
18. The non-transitory computer-readable medium of claim 16, the
instructions when executed further causing the processor to perform
steps including: determining a second correlation metric between a
second portion of the first audio signal and a second portion of
the second audio signal captured during a second time interval;
responsive to determining that the second correlation metric does
not exceed the first predefined threshold, determining whether the
first microphone is wet but is not submerged in liquid during the
second time interval; responsive to determining that the first
microphone is wet but is not submerged during the second time
interval, storing the second portion of the second audio signal as
a second portion of the output audio signal corresponding to the
second time interval.
19. The non-transitory computer-readable medium of claim 16, the
instructions when executed further causing the processor to perform
steps including: determining a second correlation metric between a
second portion of the first audio signal and a second portion of
the second audio signal captured during a second time interval;
responsive to determining that the second correlation metric does
not exceed the first predefined threshold, determining whether the
first microphone is wet during the second time interval; responsive
to determining that first microphone is wet during the second time
interval, determining a first noise metric for the second portion
of the first audio signal and a second noise metric for the second
portion of the second audio signal during the second time interval;
and selecting between storing the second portion of the first audio
signal and the second portion of the second audio signal as a
second portion of the output audio signal corresponding to the
second time interval based on the first and second noise
metrics.
20. The non-transitory computer-readable medium of claim 19,
wherein determining if the first microphone is wet comprises:
determining a first average signal level of the second portion of
the audio signal and a second average signal level for the second
portion of the second audio signal; determining if a wind condition
is detected during the second time interval; and responsive to the
ratio of the first average signal level to the second average
signal level not exceeding the second threshold and not detecting
the wind condition, determining that the first microphone is wet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/083,266, filed Mar. 28, 2016, now U.S. Pat. No. ______,
which application claims the benefit of U.S. Provisional
Application No. 62/188,450 entitled "Automatic Microphone Selection
in a Sports Camera" to Zhinian Jing, et al., filed on Jul. 2, 2015,
the content of which is incorporated by reference in its
entirety.
BACKGROUND
Technical Field
[0002] This disclosure relates to audio capture, and more
specifically, to the selecting between multiple available
microphones in an audio capture system.
Description of the Related Art
[0003] In a camera designed to operate both in and out of water,
the audio subsystem can be stressed to the point where the
resulting signal captured by the microphone is distorted and
unnatural. The transition between the two environments can be
particularly challenging due to the impulse of splashing water.
During certain activities such as surfing, swimming, or other water
sports, transition in and out of water may occur frequently over an
extended period of time.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0004] The disclosed embodiments have other advantages and features
which will be more readily apparent from the following detailed
description of the invention and the appended claims, when taken in
conjunction with the accompanying drawings, in which:
[0005] Figure (FIG.) 1 is a block diagram illustrating an example
embodiment of an audio capture system.
[0006] FIG. 2 is a flowchart illustrating a first embodiment of a
process for selecting between audio signals from different
microphones in an audio capture system with multiple
microphones.
[0007] FIG. 3 is a flowchart illustrating a second embodiment of a
process for selecting between audio signals from different
microphones in an audio capture system with multiple
microphones.
[0008] FIG. 4 is a flowchart illustrating an embodiment of a
process for detecting a wet microphone condition.
[0009] FIG. 5 is a flowchart illustrating an embodiment of a
process for selecting a subset of microphones out of a group of
microphones.
[0010] FIG. 6A is first perspective view of an example camera
system.
[0011] FIG. 6B is second perspective view of an example camera
system.
[0012] FIG. 7 illustrates an example of a drainage enhancement
feature for an enhanced microphone in a camera system.
DETAILED DESCRIPTION
[0013] The figures and the following description relate to
preferred embodiments by way of illustration only. It should be
noted that from the following discussion, alternative embodiments
of the structures and methods disclosed herein will be readily
recognized as viable alternatives that may be employed without
departing from the principles of what is claimed.
[0014] Reference will now be made in detail to several embodiments,
examples of which are illustrated in the accompanying figures. It
is noted that wherever practicable similar or like reference
numbers may be used in the figures and may indicate similar or like
functionality. The figures depict embodiments of the disclosed
system (or method) for purposes of illustration only. One skilled
in the art will readily recognize from the following description
that alternative embodiments of the structures and methods
illustrated herein may be employed without departing from the
principles described herein.
Configuration Overview
[0015] In a first embodiment, an output audio signal is generated
in an audio capture system having multiple microphones including at
least a first microphone and a second microphone. The first
microphone includes a drainage enhancement feature structured to
drain liquid more quickly than the second microphone lacking the
drainage enhancement feature. A first audio signal is received from
the first microphone representing ambient audio captured by the
first microphone during a time interval. A second audio signal is
received from the second microphone representing ambient audio
captured by the second microphone during the time interval. A
correlation metric is determined between the first audio signal and
the second audio signal representing a similarity between the first
audio signal and the second audio signal. Responsive to the
correlation metric exceeding a predefined threshold, the first
audio signal is outputted for the time interval. Responsive to the
correlation metric not exceeding the first predefined threshold, a
first noise metric is determined for the first audio signal and a
second noise metric is determined for the second audio signal.
Responsive to the sum of the first noise metric and a bias value
being less than the second noise metric, the first audio signal is
output for the time interval. Responsive to the sum of the first
noise metric and the bias value being greater than the second noise
metric, the second audio signal is output for the time
interval.
[0016] In a second embodiment, an output audio signal is generated
in an audio capture system having multiple microphones including at
least a first microphone and a second microphone. The first
microphone includes a drainage enhancement feature structured to
drain liquid more quickly than the second microphone lacking the
drainage enhancement feature. A first audio signal is received from
the first microphone representing ambient audio captured by the
first microphone during a time interval. A second audio signal is
received from the second microphone representing ambient audio
captured by the second microphone during the time interval. A
correlation metric is determined between the first audio signal and
the second audio signal representing a similarity between the first
audio signal and the second audio signal. Responsive to the
correlation metric exceeding a first predefined threshold, the
first audio signal is output for the time interval. Responsive to
the correlation metric not exceeding the first predefined
threshold, it is determined whether the microphones are submerged
in liquid. If the microphones are not submerged, it is determined
whether the first microphone is wet. If the first microphone is
wet, the second microphone signal is output for the time interval.
Responsive to determining that first microphone is not wet or that
the microphones are submerged, a first noise metric is determined
for the first audio signal and a second noise metric is determined
for the second audio signal. Responsive to the sum of the first
noise metric and a bias value being less than the second noise
metric, the first audio signal is output for the time interval.
Responsive to the sum of the first noise metric and the bias value
being greater than the second noise metric, the second audio signal
is output for the time interval.
[0017] In another embodiment, a method determines if a first
microphone is wet in an camera system having a first microphone and
a second microphone, where the first microphone is positioned in a
recess of an inner side of a face of the camera, where the recess
is coupled to a channel coupled to a lower drain below the channel
to drain water from the recess away from the microphone via the
channel, and where the second microphone is positioned away from
the channel and the drain. A first average signal level of the
first audio signal and a second average signal level of the second
audio signal are determined over a predefined time interval. A
ratio of the first average signal level to the second average
signal level is determined. Responsive to the ratio of the first
average signal level to the second average signal level exceeding a
first threshold or detecting a wind condition, it is determined
that a wet microphone condition is not detected. Responsive to the
ratio of the first average signal level to the second average
signal level not exceeding the first threshold and not detecting
the wind condition, it is determined that the wet microphone
condition is detected.
[0018] In another embodiment, a camera comprises a lens assembly, a
substantially cubic camera housing, a first microphone, a lower
drain, an upper drain, a channel, and a second microphone. The lens
assembly directs light received through a lens window to an image
sensor. The substantially cubic camera housing encloses the lens
assembly and comprises a bottom face, left face, right face, back
face, top face, and front face. The first microphone is integrated
with the front face of the camera and positioned within a recess on
an interior facing portion of the front face. The lower drain is
below the first microphone and comprises an opening in the
substantially cubic camera housing near the front face. The lower
drain allows water that collects in the recess housing the first
microphone to drain. The upper drain is above the first microphone
and comprises an opening in the substantially cubic housing near
the front face. The upper drain allows air to enter the recess as
the water drains. The channel through the interior facing portion
of the front face couples the recess to the lower drain. The second
microphone is integrated with a rear portion of the substantially
cubic camera housing.
[0019] In yet another embodiment, an audio capture system comprises
a substantially cubic housing including a bottom face, left face,
right face, back face, top face, and front face. A first microphone
is integrated with the front face of the audio capture system and
positioned within a recess on an interior facing portion of the
front face. A lower drain below the first microphone comprises an
opening in the substantially cubic housing near the front face to
allow water that collects in the recess housing the first
microphone to drain. An upper drain above the first microphone
comprises an opening in the substantially cubic housing near the
front face to allow air to enter the recess as the water drains. A
channel through the interior facing portion of the front face
couples the recess to the lower drain. A second microphone is
integrated with a rear portion of the substantially cubic
housing.
Example Audio Capture System
[0020] FIG. 1 illustrates an example of an audio capture system 100
including multiple microphones. The audio capture system 100
includes at least one "enhanced" microphone 110, at least one
"reference" microphone 120, a microphone selection controller 130,
and an audio encoder 140. The enhanced microphone 110 includes a
drainage enhancement feature to enable water to drain from the
microphone more quickly than the reference microphone 120. The
drainage enhancement feature may be accomplished utilizing gravity
and/or surface tension forces. In various embodiments, the drainage
enhancement feature may be implemented using an inner surface
energy coating or particular hole dimensions, shapes, density,
patterns, or interior curvature or a combination of features that
affect that drainage profile of the enhanced microphone 110. The
enhanced microphone 110 can therefore recover relatively quickly
when moved from in water to out of water and therefore mitigates
the frequency response distortion leading to muffled, unnatural
sound when water is trapped on the membrane over the microphone or
obscures the acoustic pathways to the microphone. In contrast, the
reference microphone 120 includes a physical barrier between the
splashing water and a waterproof membrane over the microphone to
mitigate the impulses from splashing water. For example, in one
embodiment, the barrier comprises a plastic barrier that absorbs
some of the water impact impulse. In another embodiment, an air
buffer may exist between the barrier and the waterproof membrane
over the microphone. In another embodiment, a porting structure
traps a buffer layer of water on the outside of a waterproof
membrane over the microphone, thus creating a protective layer that
blocks splashing water from directly impacting the waterproof
membrane. Additionally, the muffling quality of water pooled on the
waterproof membrane reduces some high frequency content of the
splashing water.
[0021] In operation, both the enhanced microphone 110 and reference
microphone 120 capture ambient audio 105 and pass the captured
audio to the microphone selection controller 130. The audio
captured by the enhanced microphone 110 and the reference
microphone 120 may have varying audio characteristics due to the
different structural features of the microphones 110, 120.
Typically, the enhanced microphone 110 will have more spectral
artifacts both in open air and when operating under water due to
the drainage enhancement feature. Furthermore, the enhanced
microphone 110 may have degraded signal-to-noise in windy
conditions due to the drainage enhancement feature. However, the
enhanced microphone 110 will generally have better signal-to-noise
ratio performance out of water in non-windy conditions relative to
the reference microphone 120. Therefore, a different selection
between the enhanced microphone 110 and the reference microphone
120 may be desirable under different audio capture conditions.
[0022] The microphone selection controller 130 processes the audio
captured from the enhanced microphone 110 and the reference
microphone 120 and selects, based on the audio characteristics,
which of the audio signals to pass to the audio encoder 140. In one
embodiment, the microphone selection controller 130 operates on a
block-by-block basis. In this embodiment, for each time interval,
the microphone selection controller 130 receives a first block of
audio data from the enhanced microphone and a second block of audio
data from the reference microphone 120, each corresponding to
ambient audio 105 captured by the respective microphones 110, 120
during the same time interval. The microphone selection controller
130 processes the pair of blocks to determine which block to pass
the audio encoder 140.
[0023] In one embodiment, the microphone selection controller 130
generally operates to select the enhanced microphone 110 directly
after transitioning out of water since the enhanced microphone 110
tends to drain the water faster and has better out of water audio
quality. Furthermore, the microphone selection controller 130
generally operates to select the reference microphone 120 when in
the water and when transitioning between air and water because it
better mitigates the unnatural impulses caused by splashing
water.
[0024] The audio encoder 140 encodes the blocks of audio received
from the microphone selection controller 130 to generate an encoded
audio signal 145.
[0025] In an embodiment, the microphone selection control 130
and/or the audio encoder 140 are implemented as a processor and a
non-transitory computer-readable storage medium storing
instructions that when executed by the processor carry out the
functions attributed to the microphone selection controller 130
and/or audio encoder 140 described herein. The microphone selection
controller 130 and audio encoder 140 may be implemented using a
common processor or separate processors. In other embodiments, the
microphone selection controller 130 and/or audio encoder 140 may be
implemented in hardware, (e.g., with an FPGA or ASIC), firmware, or
a combination of hardware, firmware and software.
[0026] In an embodiment, the audio capture system 100 is
implemented within a camera system such as the camera 500 described
below with respect to FIG. 5. Such a camera may use the encoded
audio 145 captured by the audio capture system 100 as an audio
channel for video captured by the camera. Thus, the audio capture
system 100 may capture audio in a manner that is concurrent and
synchronized with corresponding frames of video.
[0027] FIG. 2 is a flowchart illustrating an embodiment of a
process for selecting between an enhanced microphone 110 and a
reference microphone 120. A correlation metric is determined 202
between signal levels of audio blocks captured by the enhanced
microphone 110 and reference microphone 120 respectively. The
correlation metric represents a similarity between a first audio
signal captured from the enhanced microphone 110 during a time
interval and a second audio signal captured from the reference
microphone 120 during the same time interval. Generally, the
signals will be well-correlated in the absence of wind noise, but
will be poorly correlated when wind noise is present. Thus, the
correlation metric may operate as a wind detector. In one
embodiment, the correlation metric comprises a value from 0 to 1
where a correlation metric of 1 represents a situation where there
is no wind, and a correlation metric of 0 means that the captured
audio is entirely wind noise. In one embodiment, the correlation
metric is determined using a correlation function that includes a
regularization term y to handle low level signals. For example, in
one embodiment, the correlation function is given by:
X=max(0, .SIGMA..sub.n=0.sup.N-1(L[n]+.gamma.)*(R[n]n+.gamma.))
(1)
where (*) represents a scalar multiplication, N is the block size,
y is the regularization term (e.g., y=0.001), and L[n] and R[n] are
the samples from the enhanced microphone and reference microphone
respectively. The max operator constrains the correlation metric X
to be in the range 0 and +1. In one embodiment, the correlation
metric is calculated over a predefined spectral range (e.g.,
600-1200 Hz). Using a restricted range beneficially eliminates or
reduces artifacts caused by vibration (which typically occur at low
frequencies) and reduces the amount of processing relative to
calculating the metric over the full frequency spectrum. In one
embodiment, the correlation metric is updated at a frequency based
on the audio sample rate and sample block size. For example, if a
32 kHz sampling rate is used with a block size of 1024 samples, the
correlation metric may be updated approximately every 32
milliseconds. In one embodiment, the correlation metric is smoothed
over time.
[0028] The correlation metric is compared 204 to a predefined
threshold. In one embodiment, the predefined threshold may changes
between two or more predefined thresholds depending on the previous
state (e.g., whether the reference microphone or enhanced
microphone was selected) to include a hysteresis effect, For
example if for the previously processed block, the correlation
metric exceeded the predefined threshold (e.g., a predefined
threshold of 0.8) indicating that low wind noise detected, then the
predefined threshold is set lower for the current block (e.g. 0.7).
If for the previously processed block, the correlation metric did
not exceed the predefined threshold (e.g., a predefined threshold
of 0.8), indicating that high wind noise was detected, then the
predefined threshold for the current block is set higher (e.g., to
0.8),
[0029] If the correlation metric exceeds 204 a predefined
threshold, then the enhanced microphone 110 is selected because it
typically has better signal-to-noise ratio. If the correlation
metric does not exceed 204 the predefined threshold, noise metrics
are determined for the audio signals captured by the enhanced
microphone 110 and the reference microphone 120. Under some
conditions, it may be reasonably presumed that both microphones
110, 120 pick up the desired (noiseless) signal at approximately,
the same level and if one of the microphones is slightly blocked,
then the correlation metric will still be relatively high
indicating that there is low wind. Furthermore, it may be
reasonably presumed that noise from the effects of wind or water is
local to each microphone and that the noise will not destructively
cancel out the signal. Based on these assumptions, the microphone
that is louder during a low correlation condition is determined to
be the microphone that has the noise. Thus, in one embodiment, the
noise metrics simply comprise root-mean-squared amplitude levels of
the enhanced and reference microphones over a predefined time
period. For example, the predefined time period may include a
sliding time window that includes the currently processed block and
a fixed number of blocks prior to the current block (e.g., an
approximately 4 second window). In another embodiment, a
recursive-based RMS value is used (e.g., with a time constant of
approximately 4 seconds). In one embodiment, the noise metric is
based on equalized amplitude levels of the microphones. The
equalization levels are set so that the microphones have similar
amplitude characteristics under normal conditions (e.g., non-windy
and non-watery conditions). In one embodiment, the noise metric is
measured across substantially the entire audible band (e.g.,
between 20 Hz and 16 kHz).
[0030] If the sum of the noise metric for the enhanced microphone
110 and a bias value is less than the noise metric for the
reference microphone 120, then the microphone selection controller
130 selects 212 the enhanced microphone. On the other hand, if the
sum of the noise metric for the enhanced microphone 110 and the
bias value is not less than (e.g., greater than) the noise metric
for the reference microphone 120, then the microphone selection
controller 130 selects 212 the reference microphone 120.
[0031] In one embodiment, the bias value may comprise either a
positive or negative offset that is dynamically adjusted based on
the correlation metric. For example, if the correlation metric is
below a lower threshold (e.g., 0.4), then a first bias value is
used which may be a positive bias value (e.g., 10 dB). If the
correlation metric is above an upper threshold (e.g., 0.8), then a
second bias value is used which may be a negative bias value (e.g.,
-6 dB). If the correlation metric is between the lower threshold
(e.g., 0.4) and the upper threshold (e.g., 0.8), the bias value is
a linear function of the correlation metric X For example, in one
embodiment, the bias value is given by:
bias = { bias 1 , X .ltoreq. Th L bias 1 - bias 2 Th L - Th U ( X -
Th L ) + bias 1 , Th L < X < Th U bias 2 , X .gtoreq. Th U (
2 ) ##EQU00001##
where bias.sub.1 is the first bias value used when the correlation
metric X is below the lower threshold Th.sub.L and bias.sub.2 is
the second bias value used when the correlation metric X is above
the upper threshold Th.sub.U.
[0032] In one embodiment, a hysteresis component is additionally
included in the bias value. In this embodiment, the bias value is
adjusted up or down depending on whether the reference microphone
120 or the enhanced microphone 110 was selected for the previous
block, so as to avoid switching between the microphones 110, 120
too frequently. For example, in one embodiment, if the enhanced
microphone 110 was selected for the previous block, an additional
hysteresis bias (e.g., 5 db) is subtracted from the bias value to
make it more likely that the enhanced microphone 110 will be
selected again as shown in the equation below:
bias = { bias 1 - bias H , X .ltoreq. Th L bias 1 - bias 2 Th L -
Th U ( X - Th L ) + bias 1 - bias H , Th L < X < Th U bias 2
- bias H , X .gtoreq. Th U ( 3 ) ##EQU00002##
where bias.sub.H is the hysteresis bias.
[0033] On the other hand, if the reference microphone 120 was
selected for the previous block, the additional hysteresis bias
(e.g., 5 dB) is added to the bias value to make it more likely that
the reference microphone is selected again as shown in the equation
below:
bias = { bias 1 - bias H , X .ltoreq. Th L bias 1 - bias 2 Th L -
Th U ( X - Th L ) + bias 1 + bias H , Th L < X < Th U bias 2
- bias H , X .gtoreq. Th U ( 4 ) ##EQU00003##
[0034] The bias value takes into account that not all wind level is
created equal. It is possible to have wind that is softer, but
generates more perceptive noise, than a louder wind. With high
amounts of wind (low correlation metric), the enhanced microphone
110 tends to generate more perceptive noise than the reference
microphone 120 during high wind condition due to the drainage
enhancement feature. Thus, the bias value is used to penalize the
enhanced microphone 110 for low correlation metrics.
[0035] FIG. 3 is a flowchart illustrating another embodiment of a
process for selecting between an enhanced microphone 110 and a
reference microphone 120. A correlation metric is determined 302
between signal levels of audio blocks captured by the enhanced
microphone 110 and reference microphone 120 respectively. If the
correlation metric exceeds 304 a predefined threshold, then the
enhanced microphone 110 is selected because it typically has better
signal-to-noise ratio. If the correlation metric does not exceed
304 the threshold, it is determined 306 if the microphones are
submerged in liquid (e.g., water). The predefined threshold may be
determined in the same manner described above.
[0036] In one embodiment, a water submersion sensor may be used to
determine if the microphones are submerged. In other embodiment (in
which the audio capture system is integrated with a camera), an
image analysis may be performed to detect features representative
of the camera being submerged in water. For example, detecting
color loss may be indicative of the camera being submerged because
it causes exponential loss of light intensity depending on
wavelength. Furthermore, crinkle patterns may be present in the
image when the camera is submerged because the water surface can
form small concave and convex lenses that create patches of light
and dark. Additionally, light reflecting off particles in the water
creates scatter and diffusion that can be detected to determine if
the camera is submerged. In yet another embodiment, water pressure
on the microphone's waterproof membrane may be detected because the
waterproof membrane will deflect under external water pressure.
This causes increased tension which shifts the waterproof
membrane's resonance higher from its nominal value and can be
detected in the microphone signal. Furthermore, the deflection of
the waterproof membrane will results in a positive pressure on and
deflection of the microphone membrane which could manifest itself
as a shift in microphone bias. Additionally, a sensor could be
placed near the waterproof membrane to detect an increase in shear
force caused by deflection of the waterproof membrane that is
indicative of the microphone being submerged.
[0037] If the microphones are not submerged, then it is determined
316 whether the enhanced microphone 110 is wet (e.g., not
sufficiently drained after being removed from water). In one
embodiment, the wet microphone condition can be detected by
observing spectral response changes over a predefined frequency
range (e.g., 2 kHz-4 kHz) or by detecting the sound pattern known
to be associated with a wet microphone as compared to a drained
microphone. For example, in one embodiment the spectral features
associated with a wet (undrained) microphone can be found through
empirical means. In general, when a microphone membrane is wet,
higher frequency sounds are attenuated because the extra weight of
the water on the membrane reduces the vibration of the membrane.
Thus, the water generally acts as a low pass filter. An example of
a process for detecting wet microphones is described in FIG. 4
below. In one embodiment, spectral changes can be monitored based
on the measured known drain time constant differences between the
microphone geometries. If the enhanced microphone 110 is wet (e.g.,
not sufficiently drained), then the reference microphone 120 is
selected 320. Otherwise, if the microphones are submerged or if the
enhanced microphone 110 is not wet, then noise metrics are
determined 310 for the audio blocks captured by the enhanced
microphone 110 and the reference microphone 120. The noise metrics
may be determined in the same manner as described above in FIG. 2.
If the sum of the noise metric for the enhanced microphone 110 and
a bias value is less than the noise metric for the reference
microphone 120, then the microphone selection controller 130
selects 314 the enhanced microphone. On the other hand, if the sum
of the noise metric for the enhanced microphone 110 and the bias
value is not less than the noise metric for the reference
microphone 120, then the microphone selection controller 130
selects 320 the reference microphone 120. The bias value may be
determined based on equations (2)-(4) described above.
[0038] FIG. 4 is a flowchart illustrating an embodiment of a
process for detecting a wet microphone. Generally, water on a
microphone has a transfer function approximating a low pass filter.
The amount of attenuation and the cutoff frequency of the wet
microphone transfer function is dependent on how much water is on
the microphone. Particularly, the more water on the microphone
membrane, the greater the attenuation and the lower the cutoff
frequency. This phenomenon is due to the added mass of the water on
the microphone membrane dampening the movement of the membrane. In
one embodiment, root-mean-squared (RMS) signal levels of the audio
blocks captured by the enhanced microphone 110 and reference
microphone 120 are calculated 402 across a predefined frequency
range (e.g., 2 kHz-4 kHz). A smoothing filter may be applied 404 to
smooth the a ratio of the enhanced microphone RMS signal level to
the reference microphone RMS signal level over time. If it is
determined 406 that the ratio of the enhanced microphone RMS signal
level to the reference microphone RMS signal level is above a
predefined threshold, then the wet microphone is not detected 412.
Otherwise, if it is determined 406 that the ratio of the RMS signal
levels is not above the predefined threshold, it is determined 408
if wind is present since the presence of wind can result in similar
RMS ratios. The presence of wind can be determined based on, for
example, a detection signal from a wind detector that determines
the presence of wind based on a correlation metric X as described
above. If it is determined 408 that wind noise threshold is met
(i.e., the correlation metric is less than a predefined threshold),
then the wet microphone is not detected 412. Otherwise, if the wind
noise threshold is not met (i.e., the correlation metric is greater
than a predefined threshold), then the wet microphone condition is
detected 410.
[0039] In embodiments where there are two or more enhanced
microphones 110 and two or more reference microphones 120, the
selection algorithm described above may be applied to a group of
enhanced microphones 110 and group of reference microphones 120
instead of a single enhanced microphone 110 and single reference
microphone 120. In this embodiment, the enhanced microphone signal
and reference microphone signal inputted to the processes above may
comprise, for example, an average of all of the enhanced
microphones and the reference microphones respectively. Then the
processes described above select either the enhanced microphone
group or the reference group. Furthermore in one embodiment, once
either the enhanced microphones 110 or reference microphones 120
are selected, a separate selection algorithm may be applied to
select an audio block from one of the microphones in the selected
group to provide to the audio encoder 140 (e.g., the signal with
the lowest noise).
[0040] In another embodiment, a process selects a subset of
microphones out of a group of microphones that may include
reference microphones or enhanced microphones. FIG. 5 illustrates
an embodiment of a process performed by the microphone selection
controller 130 for choosing N microphones out of a group of M
microphones. Audio signals are received 502 from each of the
microphones in the group. Adverse conditions such as wind (e.g.,
low correlation value) or wet microphone (e.g., using the process
of FIG. 4) are detected 504 if present. If no adverse conditions
(e.g., wind, water, etc.) are detected, the microphone selection
controller 130 selects 506 N microphones in the group of M
microphones that are pre-identified as being preferred microphones.
If adverse conditions are detected (e.g., wind or water) the RMS
levels of each of the M microphones are measured 508 and a bias
value is added to each microphone. In one embodiment, the bias
value is determined based on the bias equations (2)-(4) described
above. In alternative embodiments, the bias value for each
microphone may be different depending on the configuration of each
microphone. For example, in one embodiment, the bias function can
be a function of the correlation metric, the RMS values of all
other microphones and the determination of whether or not the
microphone is under water. Then, the N microphones having the
lowest sums of their respective bias values and RMS levels are
selected 510. Mathematically, the process described above can be
represented by the following equations:
J .fwdarw. = [ J 1 J 2 J M ] = [ f 1 ( X , R 1 , R 2 , , R M ) f 2
( X , R 1 , R 2 , , R M ) f M ( X , R 1 , R 2 , , R M ) ]
##EQU00004##
where the microphone selection controller 130 picks the N
microphones having the smallest cost value of J and where J.sub.i
is a cost value associated with the ith microphone, X is the
correlation metric, R is the RMS value of the ith microphone, and
f.sub.i is a predefined cost function.
[0041] In the case of only a single reference microphone 120 and a
single enhanced microphone 120, f.sub.1(X, R.sub.1,
R.sub.2)=R.sub.1+g(X) and f.sub.2(X, R.sub.1, R.sub.2)=R.sub.2
where g(X) is the piecewise linear function described in the bias
equations above, f.sub.1 is the cost function for the enhanced
microphone 110 and f.sub.2 is the cost function for the reference
microphone 120. In one embodiment, a hysteresis bias may also be
included as described above, except with potentially different
thresholds, depending on the configuration.
Example Camera System Configuration
[0042] FIGS. 6A-6B illustrate perspective views of an example
camera 600 in which the audio capture system 100 may be integrated.
The camera 600 comprises at least one cross-section having four
approximately equal length sides in a two-dimensional plane.
Although the cross-section is substantially square, the corners of
the cross-section may be rounded in some embodiments (e.g., a
rounded square or squircle). The exterior of the square camera 600
includes 6 surfaces (i.e. a front face, a left face, a right face,
a back face, a top face, and a bottom face). In the illustrated
embodiment, the exterior surfaces substantially conform to a
rectangular cuboid, which may have rounded or unrounded corners. In
one example embodiment, all camera surfaces may also have a
substantially square (or rounded square) profile, making the square
camera 600 substantially cubic. In alternate embodiments, only two
of the six faces (e.g., the front face 610 and back face 640) have
equal length sides and the other faces may be other shapes, such as
rectangles. The camera 600 can have a small form factor (e.g. a
height of 2 cm to 9 cm, a width of 2 cm to 9 cm, and a depth of 2
cm to 9 cm) and is made of a rigid material such as plastic,
rubber, aluminum, steel, fiberglass, or a combination of materials.
In other embodiments, the camera 600 may have a different form
factor.
[0043] In an embodiment, the camera 600 includes a camera lens
window 602 surrounded by a front face perimeter portion 608 on a
front face 610, an interface button 604 and a display 614 on a top
face 620, an I/O door 606 on a side face 630, and a back door 612
on a back face 640. The camera lens window 602 comprises a
transparent or substantially transparent material (e.g., glass or
plastic) that enables light to pass through to an internal lens
assembly. In one embodiment, the camera lens window 602 is
substantially flat (as opposed to a convex lens window found in
many conventional cameras). The front face 610 of the camera 600
furthermore comprises a front face perimeter portion 608 that
surrounds the lens window 602. In one embodiment, the front face
perimeter portion 608 comprises a set of screws to secure the front
face perimeter portion 608 to the remainder of the housing of the
camera 600 and to hold the lens window 602 in place.
[0044] The interface button 604 provides a user interface that when
activated enables a user to control various functions of the camera
600. For example, pressing the button 604 may control the camera to
power on or power off, take pictures or record video, save a photo,
adjust camera settings, or perform any other action relevant to
recording or storing digital media. In one embodiment, the
interface button 604 may perform different functions depending on
the type of interaction (e.g., short press, long press, single tap,
double tap, triple tap, etc.) In alternative embodiments, these
functions may also be controlled by other types of interfaces such
as a knob, a switch, a dial, a touchscreen, voice control, etc.
Furthermore, the camera 600 may have more than one interface button
604 or other controls. The display 614 comprises, for example, a
light emitting diode (LED) display, a liquid crystal display (LCD)
or other type of display for displaying various types of
information such as camera status and menus. In alternative
embodiments, the interface button 604, display 606, and/or other
interface features may be located elsewhere on the camera 600.
[0045] The I/O door 606 provides a protective cover for various
input/output ports of the camera 600. For example, in one
embodiment, the camera 600 includes a Universal Serial Bus (USB)
port and/or a High-Definition Media Interface (HDMI) port, and a
memory card slot accessible behind the I/O door 606. In other
embodiments, additional or different input/output ports may be
available behind the I/O door 606 or elsewhere on the camera
600.
[0046] The back door 612 provides a protective cover that when
removed enables access to internal components of the camera 600.
For example, in one embodiment, a removable battery is accessible
via the back door 612.
[0047] In some embodiments, the camera 600 described herein
includes features other than those described below. For example,
instead of a single interface button 604, the square camera 600 can
include additional buttons or different interface features such as
a speakers and/or various input/output ports.
[0048] In one embodiment, the reference microphone 110 is
integrated with or near the back door 612 of the camera 600 such
that it is positioned near the rear of the camera 600, and the
enhanced microphone is integrated with the front face 610 of the
camera 600 such that it is positioned near the front of the camera
600.
[0049] FIG. 7 illustrates an example of a front face perimeter
portion 608 of a camera 600 with an integrated drain enhancement
feature in the form of a channel 702 between a recess 704 where the
enhanced microphone 110 (not shown) is positioned, and one or more
drains (e.g., an upper drain structure 708 and a lower drain
structure 706, each of which may comprise a single drain or
multiple drains) to enable liquid to drain. Microphone ports 710
provide openings to let sound reach the microphone(s) housed in
recess 704. In one embodiment, the upper drain structure 708 is
positioned above the channel 702 and the lower drain structure 706
is positioned below the channel 702. The lower drain structure 706
is generally much larger than the upper drain structure 708.
[0050] When the camera 600 is submerged the entire channel 702
generally fills with water. When the camera 600 emerges from the
water, the large mass of water in the channel 702 flows out through
the lower drain structure 706 through the force of gravity. This
pulls air in through upper drain structure 708 and clears water
from the recess 704, the upper drain structure 708, and/or the
microphone ports 710, thus allowing the microphone to resume normal
acoustic performance.
Additional Configuration Considerations
[0051] Throughout this specification, some embodiments have used
the expression "coupled" along with its derivatives. The term
"coupled" as used herein is not necessarily limited to two or more
elements being in direct physical or electrical contact. Rather,
the term "coupled" may also encompass two or more elements are not
in direct contact with each other, but yet still co-operate or
interact with each other, or are structured to provide a drainage
path between the elements.
[0052] Likewise, as used herein, the terms "comprises,"
"comprising," "includes," "including," "has," "having" or any other
variation thereof, are intended to cover a non-exclusive inclusion.
For example, a process, method, article, or apparatus that
comprises a list of elements is not necessarily limited to only
those elements but may include other elements not expressly listed
or inherent to such process, method, article, or apparatus.
[0053] In addition, use of the "a" or "an" are employed to describe
elements and components of the embodiments herein. This is done
merely for convenience and to give a general sense of the
invention. This description should be read to include one or at
least one and the singular also includes the plural unless it is
obvious that it is meant otherwise.
[0054] Finally, as used herein any reference to "one embodiment" or
"an embodiment" means that a particular element, feature,
structure, or characteristic described in connection with the
embodiment is included in at least one embodiment. The appearances
of the phrase "in one embodiment" in various places in the
specification are not necessarily all referring to the same
embodiment.
[0055] Upon reading this disclosure, those of skill in the art will
appreciate still additional alternative structural and functional
designs as disclosed from the principles herein. Thus, while
particular embodiments and applications have been illustrated and
described, it is to be understood that the disclosed embodiments
are not limited to the precise construction and components
disclosed herein. Various modifications, changes and variations,
which will be apparent to those skilled in the art, may be made in
the arrangement, operation and details of the method and apparatus
disclosed herein without departing from the spirit and scope
defined in the appended claims.
* * * * *